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Cold-laps or Crack on Surface of Big Bore Pipe

02/21/2007 4:57 AM

I have some bad big bore pipes as show. The pipes are same heat number and size is 500 OD x 38mm. The defects are detected by MPI. UT has been used to verify the depth - 6mm max. Some body said that the defect are cracks and some other said that they are coldlaps. What is correct type of the defects? And, what are the cause of the defects?

Re: Cold-laps or Crack on Surface of Big Bore Pipe

02/22/2007 1:16 PM

Hi Dao Huu Xuan:

It is hard to tell for sure in the top photo the defect appears to be a crack or also known as a seam. The bottom photo looks very much like cold lapping.

These defects occur while rolling the steel. Billets of steel are rolled into plates and plates are rolled into sheets with appropriate heating in-between to anneal the metal. Many different types of rolling defects can occur such as overfill, scratches, gorges, seams, and laps. You should contact your material supplier and find out what quality control process is in place.

Re: Cold-laps or Crack on Surface of Big Bore Pipe

02/22/2007 10:10 PM

Hi MechTech,

Thank you for your discussion. The pipe is seamless and cast product. The top photo show the defect look like crack due to heating. But, bottom photo looks very much like cold lapping. The subsequent question is that: why cast product contains cold lapping?

Re: Cold-laps or Crack on Surface of Big Bore Pipe

Below is what they have to say about cold lapping. The picture on the web site does not look like what you have but the description matches it pretty well.
I agree whole heartedly with Keith, reject the entire heat and start investigating your suppliers QC specifications. I hope this helps.

MechTech

"Cold Shut or Cold Lap:

A linear discontinuity with rounded edges. The defect has a characteristic appearance and may vary in depth. In the mildest case, it may consist merely of a shallow groove with rounded edges. A cold shut occurs on wide surfaces of the casting, in thin sections that are difficult to fill or where two streams of metal converge in the mold due to the sequence of filling."

Re: Cold-laps or Crack on Surface of Big Bore Pipe

02/22/2007 2:10 PM

I suggest you reject the entire heat. Its an obvious and major defect and should have NEVER made it to finished pipe. You should also hire a consultant in pipe Q/A and get a thorough overhaul of vendor Q/A process and proof that it is working before accepting (provisionally) any more pipe.